The fourth volume of the Collected Works is devoted to Wigner's contribution to physical chemistry, statistical mechanics and solid-state physics. In his annotation to the first part, N. Balazs clearly points out Wigner's role in early quantum chemistry and applied statistical mechanics. One corner stone was his introducing of what is now called the Wigner function, and his paper on adiabatic perturbations foreshadowed later work on Berry phases. Although few in number, Wigner's articles on solid-state physics laid the ground for the modern theory of the electronic structure of metals. W. Kohn writes about this in his annotation to Part 2 of the book and he also points out Wigner's great influence in the development of solid-state theory.